The present invention relates to a reciprocating-piston engine having an electromechanical converter which can be operated as an electrical generator and/or as an electric motor, and to a system having a reciprocating-piston engine.
EP 1 223 316 B1 discloses a reciprocating-piston engine, in the crank chamber of which there is arranged an electromechanical converter which has the function of an electric motor and/or of an electrical generator. Magnetic-field-generating elements in the form of permanent magnets are arranged on a crankshaft, which is held rotatably in the crank chamber by way of a bearing cover attached to a cylinder block. The permanent magnets are inserted fixedly, by way of an interference fit, in recesses of the balancing weights of the crankshaft, and serve as additional balancing weights. Coils are held in static fashion in the crank chamber on the bearing cover. During rotation of the crankshaft, the permanent magnets rotate relative to the static coils, whereby a voltage is induced in the coils owing to the electromagnetic interaction between the permanent magnets and the coils, and the electromechanical converter acts as a generator. By feeding an alternating voltage to the coils, in particular from a battery, an electromagnetic force is exerted on the permanent magnets, and by way of the electromagnetic interaction, the electromechanical converter acts as an electric motor. Since the coils are held on the bearing cover, the coils can, together with the bearing cover, be attached to and removed from the cylinder block, which permits simple assembly and disassembly or exchange of the coils. It is also described that, for improved cooling, the coils are arranged in the region of the oil pan of the crank chamber and dip into the oil contained in the oil pan, whereby cooling of the coils by way of the oil is made possible.
In the case of the reciprocating-piston engine known from the prior art, the magnetic-field-generating elements in the form of permanent magnets are arranged in the balancing weights of the crankshaft by being fixed in recesses of the balancing weights by way of an interference fit. The arrangement of the permanent magnets in the provided recesses of the balancing weights has the advantage that the permanent magnets serve as additional balancing weights, and therefore an additional increase in weight of the crankshaft owing to the permanent magnets, in relation to a conventional crankshaft, can be avoided. Said arrangement however also has several disadvantages. Crankshafts are generally of unipartite form and are manufactured either in a casting process, in particular from spheroidal graphite iron, tempering steel or nitriding steel, or in a pressure forming process. The materials suitable for the production of highly loadable crankshafts, and used in mass production nowadays, are magnetizable. In other words, conventional crankshafts have ferromagnetic or ferrimagnetic characteristics. They are thus attracted by the magnetic pole of an external magnetic field without a high level of residual magnetization remaining; in other words, they are magnetically soft, or themselves give rise, after magnetization, to a static magnetic field because they are magnetically hard and exhibit high remanence. Conventional crankshafts exhibit only limited suitability for the arrangement of permanent magnets in recesses of balancing weights by way of an interference fit, because the permanent magnets give rise to magnetization of the crankshaft as a whole, and the generation of a directed magnetic field, which runs in a defined manner, for the efficient induction of a voltage in the coils surrounding the crankshaft is not possible. Furthermore, there is the risk of demagnetization of the permanent magnets. The arrangement described in EP 1 223 316 B1 systemically exhibits low electrical power owing to the arrangement of the permanent magnets. Since a crankshaft balancing weight, in order to perform its generic function, extends only in a range situated opposite the adjacent connecting-rod bearing, said range generally being considerably less than 120° and thus encompassing less than one third of the rotational circumference, the permanent magnets in the balancing weight can also only be arranged in said partial range, whereby the maximum electrical power of the electromechanical converter is severely limited. Furthermore, the arrangement of the permanent magnets by way of an interference fit in the crankshaft is cumbersome from a production aspect, and there is the risk of the permanent magnets becoming detached at high crankshaft rotational speeds.